During 1978 important and exciting new data was obtained on the mechanisms and genetic control of antibody structure, initiating events in the immune response and regulatory processes for humoral cytotoxicity reactions. Particularly notable was the demonstration that 3 separate gene regions control kappa chain composition and the fact that these regions were separated by null genetic material that did not code for immunoglobulin structure. Furthermore, the RNA transcribed from this gene region contained similar null regions. Thus, kappa chain V and C region in RNA must be spliced together during nuclear RNA processing. Clearly, these splicing processes are of key importance in regulation of antibody composition and specificity. Stimulation of cells to make antibody is multifaceted, and recent studies indicate a specific order in the cellular changes characterizing B cell maturation. These surface changes apparently regulate susceptibility to antigen stimulation and reflect the type of antibody that will be produced. Furthermore, detailed studies of the regulation by various T cell subpopulations of B cells antibody formation revealed a soluble helper factor specific for tetanus antibody that is distinct from that regulating immunoglobulin synthesis. Similar systems were found in studies of lymphoid cytotoxicity. Both T cell and monocytes regulated the development and expression of lymphoid cell cytotoxicity. In addition, this regulation can be mediated in part by soluble factors. Cells are normally present in various stages of maturation and require specific stimuli and help to become fully effective cytotoxic cells. Investigations of monocytes and macrophages reveal subpopulations with different functions, e.g. chemotaxis and phagocytosis being more prominent in the larger monocytes and antibody dependent cellular cytotoxicity more prominent in the smaller population.